1. Field of the Invention
This invention refers to a secondary cell module and the method of its production and, although not specially limited to these, relates to a high capacity secondary cell module and the method of its production which is the most appropriately used for uses in electric automobiles, UPS (uninterruptible power equipment), load leveling of electricity, etc.
2. Related Art Statement
In recent years, electric automobiles are attracting attention for reason of environmental problems, etc. and there is an increasing need for a high capacity and low cost secondary cell of maintenance-free for the purpose of securing electricity at time of disaster such as earthquakes, etc. and an efficient use, etc. of electricity at night.
In this connection, also in the past, for example, a secondary cell module of high capacity in which multiple lithium ion secondary cells (electric cell) are connected in series with each other in order to form a combination cell and this combination cell incorporated into a casing has been proposed (each official report of JP H07-282, 841 A, JP H08-96, 987 A and JP H08-96, 841 A). And in these secondary cell modules, the contour of each lithium ion secondary cell (electric cell) which forms its combination cell is formed in block type by laminating, using separators in between, its positive electrode on metal material on which an active material compound is applied and its negative electrode of metal material on which an active material compound is applied, more than 2 of these electric cells are connected in series, and each electric cell of a combination cell contained in a container body (casing) is divided by partition walls installed in the container body, thereby each electric cell being insulated from each other, both of these being considered appropriate for securing a high capacity cell.
In this type of secondary cell module, however, the problem is that the cell cannot but be a block shape of a comparatively large contour because the container body must contain multiple electric cells of block shape, which limits the degree of freedom in designing the shape of the container body as well as the container becoming inevitably large because of need of partition walls for insulating each electric cell which forms a combination cell, thus increasing its weight by that degree.
And this type of problem of a secondary cell module may become a fatal problem in case it is used in an electric automobile. That is, in an electric automobile, the set-up space for installing a secondary cell module is quite limited, it becomes necessary to make a big change in the relative set-up positions of other parts in case the secondary cell module becomes too large, and also there is a problem that the fuel cost efficiency of an automobile drops if the weight of the secondary cell module increases, all of which require a cell of small size and light weight in addition to a high degree of freedom in designing its shape.
In this connection, for example, when a secondary cell of lithium ion is used in an electric automobile, a high capacity is required in view of a safe and stable running as well as securing a long running distance by one electrification, and in order to achieve this at a high level, a cell of a higher capacity is desired. In uses where this kind of high capacity is desirable, although not limited to automobiles, a large electric current discharge sometimes occurs when a secondary cell of lithium ion is in use, in which case a large amount of heat which is in proportionate to (electric current)×(internal resistance) generates and this heat diffuses by a large amount from the surface of an electrode in the direction of normal line.
Therefore, in case a secondary cell module of a high capacity if formed by composing a combination cell by connecting, specifically, multiple secondary cells of lithium ion with each other and by incorporating this combination cell into a casing, the larger the number of electric cells to be connected becomes and the higher its capacity becomes, the more important the problem becomes of how easily to diffuse the heat generated in each electric cell so that it does not accumulate, and this problem cannot be coped with only by shaping the cell in a sheet type with the area of its plane surface being made larger against the its thickness or by utilizing each terminal which is drawn outside from the internal electrode couple in order to radiate the heat.